Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of both gaseous and solid material, such as, for example, particulate matter. Particulate matter may include ash and unburned carbon particles and may sometimes be referred to as soot.
Due to increased environmental concerns, exhaust emission standards have become more stringent. The amount of particulate matter and gaseous pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. In order to meet these emissions standards, engine manufacturers have pursued improvements in several different engine technologies, such as fuel injection, engine management, and air induction, to name a few. In addition, engine manufacturers have developed devices for treatment of engine exhaust after it leaves the engine.
Engine manufacturers have employed exhaust treatment devices called particulate traps to remove the particulate matter from the exhaust flow of an engine. A particulate trap may include a filter designed to trap particulate matter. The use of the particulate trap for extended periods of time, however, may enable particulate matter to accumulate on the filter, thereby causing damage to the filter and/or a decline in engine performance.
One method of restoring the performance of a particulate trap may include regeneration. Regeneration of a particulate trap filter system may be accomplished by thermal regeneration, which may include increasing the temperature of the filter and the trapped particulate matter above the combustion temperature of the particulate matter, thereby burning away the collected particulate matter and regenerating the filter system. This increase in temperature may be effectuated by various means. For example, some systems employ a heating element (e.g., an electric heating element) to directly heat one or more portions of the particulate trap (e.g., the filter material or the external housing). Other systems have been configured to heat the exhaust gases upstream from the particulate trap, allowing the flow of the heated gases through the particulate trap to transfer heat to the particulate trap. For example, some systems may alter one or more engine operating parameters, such as air/fuel mixture, to produce exhaust gases with an elevated temperature. Running an engine with a “rich” air/fuel mixture can elevate exhaust gas temperature. Other systems heat the exhaust gases upstream from the particulate trap, with the use of a burner that creates a flame within the exhaust conduit leading to the particulate trap.
In some systems, regeneration may be performed continually. In other systems, regeneration may be performed periodically. That is, after a trigger condition occurs, a thermal regeneration system may initiate regeneration in response to the trigger condition. Some systems are configured to initiate regeneration in response to a single type of trigger condition, such as the operation of the engine for a predetermined amount of time or a pressure characteristic of the exhaust system (e.g., backpressure in the exhaust system). Some systems are configured to initiate regeneration in response to measurements of the amount of particulate matter accumulated in the particulate trap. For example, one such regeneration system is disclosed by U.S. Pat. No. 4,477,771 issued to Nagy et al. on Oct. 16, 1984 (“the '771 patent”). The '771 patent discloses a regeneration system configured to initiate regeneration in response to a determination of power loss of microwaves transmitted through the filter medium within a particulate trap.
The system of the '771 patent may be configured to initiate regeneration in response to a determination of power loss of a radio frequency (RF) signal. However, the system of the '771 patent utilizes microwaves rather than low frequency RF signals. For example, the '771 patent discloses use of RF signals having frequencies on the order of 1.85 GHz (1850 MHz). Use of higher frequencies, such as the microwaves used in the '771 patent, requires system components that are more complicated and thus cost more at each stage of development and production. Further, the use of microwaves, as in the '771 patent, often requires a waveguide or resonant chamber. The requirement of such a chamber may limit the design possibilities of a particulate trap housing.
The present disclosure is directed to solving one or more of the problems described above.